Many conventional three-axis motion tables are configured so that one rotation axis P vertically supports the whole of a three-axis motion table J as shown in FIG. 10.
According to the example in FIG. 10, the single rotation axis supports the whole of the three-axis motion table J. The mechanism of a base portion B for supporting the rotation axis P (a vertically extending rotation axis) becomes large and increases the weight so as to enable the reliable support in all directions.
For example, let us consider a case of mounting an experimentally produced artificial satellite on the three-axis motion table and testing attitude control motions in the three-dimensional space. There has been a demand for possible weight saving so as to be able to simulate accurate high-speed rotational motions. The conventional three-axis motion table is contrary to such demand.
The conventional three-axis motion table is made of a casting to prevent a frame's elastic vibration as disturbance to tested models. Accordingly, the three-axis motion table is inevitably subject to a large inertia moment and needs to be driven by a hydraulic motor that provides a large torque.
In addition, the three-axis motion table must be manufactured to further improve the rigidity so that a frame's vibration frequency can be separated from an operation (attitude motion) frequency domain for an artificial satellite as a tested model. This also has been a cause of increasing the inertia moment and the weight.
Furthermore, a hydraulic motor is inappropriate for endless/limitless rotations in the same direction and involves a narrow range of adjusting rotational speeds.
Conventionally, as mentioned above, castings have been used to cause an elastic vibration at high frequencies by using highly rigid members made of castings. This makes it possible to satisfactorily distinguish between frequency domains for the operational bandwidth and the vibration domain of a manufactured three-axis motion table.
It is necessary to determine whether or not the manufactured three-axis motion table causes adjacent or overlapping frequency domains for the operational bandwidth and the elastic vibration. This determination is not performed before manufacture of actual products and has been based on a designer's so-called “intuition.” For this reason, there has been a tendency toward the safe design, i.e., using highly rigid materials to prevent vibrations. Such tendency (toward the design of using highly rigid materials) also causes the inertia moment and the weight to increase and results in heavy usage of hydraulic motors capable of a large torque.
By contrast, there is a consideration for using an electric motor having less torque than the hydraulic motor to improve the three-axis motion table's operation bandwidth. For this purpose, the inertia moment and the weight need to be suppressed. When it is supposed to configure the frame with lightweight but less rigid materials such as aluminum, the manufactured three-axis motion table causes adjacent or overlapping frequency domains for the operational bandwidth and the vibration. It is impossible to eliminate an elastic vibration signal from signals detected by a sensor mounted on the tested model using a lowpass filter and the other means.
There have been available various types of the three-axis motion table J as shown in FIG. 10 (e.g., see the three-axis attitude control system testing facility issued by National Space Development Agency of Japan (NASDA) on June, 2001). None of the proposals solves the above-mentioned problems.
The present invention has been made in consideration of the foregoing. It is therefore an object of the present invention to provide a three-axis motion table that possibly decreases inertia moments around three orthogonal axes to enable the use of an electric motor generating less output (than a hydraulic motor) and increases tracking characteristics against target signals for angles and angular speed up to a high frequency domain to enable any attitude control testing in the three-dimensional space.